Figure 2.

Phospholipid synthesis in CEPT1- and CHPT1-KO cells.A–D, U2OS and CEPT1-KO cells were cultured in choline-free media containing 1 μCi/ml [³H]choline for 3 and 6 h. [³H]Choline incorporation into PC (panel A), phosphocholine (panel B), CDP-choline (panel C), and glycerophosphocholine (GPC, panel D) was measured relative to cellular protein. E, PC synthesis in CHPT1-KO cells was measured by [³H]choline labeling for 6 h. F, PE synthesis was measured in U2OS and CEPT1-KO cells by [³H]ethanolamine (1 μCi/ml) labeling for 3 h. G and H, PS synthesis (panel G) and PS decarboxylation to PE (panel H) in U2OS and CEPT1-KO cells was measure after [³H]serine (1 μCi/ml) labeling for 3 h in serine-free media. Results in panels A–H are the mean and SD of three biological replicates. I and J, the proliferation of CEPT1- and CHPT1-KO cells cultured in medium with 1 or 10% FCS was measured over 72 h by the crystal violet staining method (59). Results are the mean and SD of six biological replicates; significance was determined by an unpaired t test with matched U2OS cell controls. CEPT1, choline/ethanolamine phosphotransferase 1; CHPT1, choline phosphotransferase 1; FCS, fetal calf serum.